public class LinkedList {
    // 2、无头双向链表实现

    static class Node{
        public int val;
        public Node prev;
        public Node next;

        public Node(int val) {
            this.val = val;
        }
    }

    public Node head;
    public Node last;

    public void display(){
      Node cur = head;
      while(cur != null){
          System.out.print(cur.val +" ");
          cur = cur.next;
      }
        System.out.println();
    }


    //头插法
        public void addFirst(int data) {
            Node node = new Node(data);
            if (head == null) {
                head = node;
                last = node;
                return;
            }
            head.prev = node;
            node.next = head;
            head = node;
        }

        //尾插法
        public void addLast(int data){
            Node node = new Node(data);
            if (head == null) {
                head = node;
                last = node;
                return;
            }
            last.next = node;
            node.prev = last;
            last = node;
        }
        //任意位置插入,第一个数据节点为0号下标
        public void addIndex(int index,int data){
        if(index < 0 || index > size()){
            throw new IndexOutOfBoundException("index 下标不合法，请检查下标的合法性！");
        }
        if(index == 0 ){
            addFirst(data);
            return;
        }
        if(index == size()){
            addLast(data);
            return;
        }
        Node node = new Node(data);
        Node cur = head;
        while (index > 0){
            cur = cur.next;
            index--;
        }
        node.prev = cur.prev;
        node.next = cur;
        cur.prev.next = node;
        cur.prev = node;
        }

        //查找是否包含关键字key是否在单链表当中
        public boolean contains(int key){
        Node cur = head;
        while(cur != null){
            if(cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;

        }
        //删除第一次出现关键字为key的节点
        public void remove(int key){
        Node cur = head;
        while(cur != null){
            if(cur.val == key){
                if(cur == head){
                    head = head.next;
                    if(head != null){
                        head.prev = null;
                    }
                }else{
                    cur.prev.next = cur.next;
                    if(cur.next != null){
                        cur.next.prev = cur.prev;
                    }else{
                        last = last.prev;
                    }
                }
                return;
            }
            cur = cur.next;
        }
        }

        //删除所有值为key的节点
        public void removeAllKey(int key){
            Node cur = head;
            while(cur != null){
                if(cur.val == key){
                    if(cur == head){
                        head = head.next;
                        if(head != null){
                            head.prev = null;
                        }
                    }else{
                        cur.prev.next = cur.next;
                        if(cur.next != null){
                            cur.next.prev = cur.prev;
                        }else{
                            last = last.prev;
                        }
                    }
                }
                cur = cur.next;
            }

        }
        //得到单链表的长度
        public int size(){
        int count = 0;
        Node cur = head;
        while(cur != null){
            count++;
            cur = cur.next;
        }
        return count;
        }

        public void clear(){
        Node cur = head;
        Node curNext = null;
        while(cur != null){
            curNext = cur.next;
            cur.prev = null;
            cur.next = null;
            cur = curNext;
        }
        head = null;
        last = null;
        }
}
